For its original military use it was manufactured under the name B 1. It has been manufactured in Czechoslovakia under its current name since 1964,[note 1] labeled as SEMTEX 1A, since 1967 as SEMTEX H and since 1987 as SEMTEX 10.

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The composition of the two most common variants differ according to their use. The 1A (or 10) variant is used for blasting, and is based mostly on crystalline PETN. The version 1AP and 2P are formed as hexagonal booster charges; a special assembly of PETN and wax inside the charge assures high reliability for detonating cord or detonator. The H (or SE) variant is intended for explosion hardening.[4]

Semtex was very similar to other plastic explosives, especially C-4, in being easily malleable; but it is usable over a greater temperature range than other plastic explosives, since it stays plastic between −40 and +60 °C; it is also waterproof. There are also visual differences: while C-4 is off-white in colour, Semtex is red or brick-orange.

Exports fell after the name became closely associated with terrorist attacks. Export of Semtex was progressively tightened and since 2002 all of Explosia's sales have been controlled by a government ministry.[7] As of 2001[update], approximately only 10 tons of Semtex were produced annually, almost all for domestic use.[3]

Also in response to international agreements, Semtex has a detection taggant added to produce a distinctive vapor signature to aid detection. First, ethylene glycol dinitrate was used, later switched to 2,3-dinitro-2,3-dimethylbutane (3,4-dinitrohexane, DMDNB) or p-mononitrotoluene, which is used currently. According to the manufacturer, the taggant agent was voluntarily being added by 1991, years before the protocol signed became compulsory.[3] Batches of Semtex made before 1990, however, are untagged, though it is not known whether there are still major stocks of such old batches of Semtex. According to the manufacturer, even this untagged Semtex can now be detected.[8] The shelf life of Semtex was reduced from 10 years before the 1990s to five years now. Explosia states that there is no compulsory tagging allowing reliable post-detonation detection of a certain plastic explosive (such as incorporating a unique metallic code into the mass of the explosive), so Semtex is not tagged in this way.[9]

On May 25, 1997, Bohumil Šole, a scientist often said to have been involved with inventing Semtex, strapped the explosive to his body and committed suicide in the Priessnitzspa of Jeseník.[10] Šole, 63, was being treated there for depression. Twenty other people were hurt in the explosion, while six were seriously injured. According to the manufacturer, Explosia, he was not a member of the team that developed the explosive.

^Various sources state that production started in 1964 or 1966. Explosia's brief historical document states it was 1964,[3] but most other credible sources state it was in 1966. Most of these also state that development was started at the same time, in response to a request from Vietnam for a counterpart to the US's construction of C-4.